Correlation of beta-lactamase production and resistance to beta-lactam antibiotics in Enterobacteriaceae.

Incidence of beta-lactamase production (using the Nitrocefin test and isoelectric focusing) was evaluated on 284 strains of ampicillin-resistant Enterobacteriaceae. Production of the various beta-lactamases was correlated with the resistance to different beta-lactam antibiotics. No obvious correlation between the beta-lactamase production and the resistance pattern was found. The most striking result was the lack of beta-lactamase production in 42.6% of the strains. About 50% or more of the Proteus morganii, Proteus vulgaris, Serratia and Enterobacter strains produced no beta-lactamases, in contrast to E. coli, Klebsiella, and Proteus rettgeri strains which produced beta-lactamases extensively. The predominant enzyme was TEM 1, while TEM 2 enzyme was extremely common in Proteus mirabilis and Proteus rettgeri. Finally, it can be concluded from our results that the production of beta-lactamases can be regarded as an important but not the sole determinant of resistance of beta-lactam antibiotics.